1. Field of the Invention
The present invention relates to a multi-cylinder engine.
2. Description of Prior Art
There is the following engine as a conventional example of the multi-cylinder engine.
An inter-cylinder wall has an upper side portion provided on its left and right both sides with inter-cylinder bosses. The inter-cylinder bosses are connected to left and right both sides of a lower side portion of the inter-cylinder wall in continuity therewith. An upper female screw is provided in one of the inter-cylinder bosses. A head bolt engages with the upper female screw in screw-thread attachment. A bearing wall of a crank shaft is formed so that it can be divided into an upper wall portion and a lower wall portion. The upper wall portion is connected to a cylinder block and has left and right both sides provided with upper wall bosses. These upper wall bosses have upper end portions connected to the left and right both sides of the lower side portion of the inter-cylinder wall in continuity therewith. A lower female screw is provided in one of the upper wall bosses. A bearing bolt engages with the lower female screw in screw-thread attachment to assemble the lower wall portion to the cylinder block.
As for this type of engine, a gas pressure produced in a combustion chamber raises up a cylinder head and lowers the lower wall portion. This results in raising the upper female screw by the head bolt and lowering the lower female screw through the bearing bolt.
However, this type of engine generally has the upper female screw and the lower female screw formed in an outer wall of the cylinder block.
The foregoing conventional technique has the following problems.
The upper female screw and the lower female screw are formed in the outer wall of the cylinder block. Therefore, the outer wall of the cylinder block extends and easily vibrates with the gas pressure produced in the combustion chamber. This enlarges the engine""s noise and shortens its useful life.
In order to solve the problem 1, like the present invention, it is effective to interpose an inner space 17 between the upper and lower female screws 9, 13 and the outer wall 14 of the cylinder block 16 as shown in FIG. 1. However, in this case, the gas pressure with which the outer wall 14 of the cylinder block 6 is burdened acts on the left and right both sides 2c, 2c of the lower side portion 2b of the inter-cylinder wall 2 as well as on lower left and right peripheral wall portions 15, 15 of a cylinder wall 1 in continuity with them in the front and rear direction. Therefore, in the event each of these portions has a reduced thickness, there is a likelihood that the following new problem will occur.
In the case where the lower left and right peripheral wall portions of the cylinder wall each has a reduced thickness, this portion undergoes a large strain to result in seizing a piston and producing a slap sound or the like.
The present invention has an object to provide a multi-cylinder engine capable of solving the above-mentioned problems.
A principal construction of the present invention is as follows.
As shown in FIG. 1, the inner space 17 is interposed between the upper and lower female screws 9, 13, which engage with the head bolt 8 and the bearing bold 12 in screw-thread attachment, respectively, and the outer wall 14 of the cylinder block 6.
As shown in FIGS. 3 and 4, the lower left and right peripheral wall portions 15, 15 of the cylinder wall 1 continue with the left and right both sides 2c, 2c of the lower side portion 2b of the inter-cylinder wall 2 in the front and rear direction. They increase their thicknesses progressively as they approach the left and right both sides 2c, 2c. 
The present invention offers the following effect.
As shown in FIG. 1, the inner space 17 is interposed between the upper and lower female screws 9, 13 and the outer wall 14 of the cylinder block 6. The gas pressure produced in the combustion chamber hardly extends and vibrates the outer wall 14 of the cylinder block 6. This decreases the engine""s noise and also elongates its useful life.
As shown in FIGS. 3 and 4, the lower left and right peripheral wall portions 15, 15 of the cylinder wall 1 continue with the left and right both sides 2c, 2c of the lower side portion 2b of the inter-cylinder wall 2 and increase their thicknesses gradually as they approach the left and right both sides 2c, 2c. Therefore, even if a large gas pressure acts on the lower left and right peripheral wall portions 15, 15 of the cylinder wall 1, it is possible to inhibit the strain of these portions with the result of prohibiting the seizure of the piston and the production of the slap sound or the like attributable to the strain of these portions.
As shown in FIG. 1, a lowermost edge 20 of a transverse water passage 18 is arranged higher than a position 19 of a piston ring at the uppermost portion of a piston head positioned at a bottom dead center. This arrangement makes it possible to secure a full height of the lower side portion 2b of the inter-cylinder wall 2 and therefore surely obtain a strength of this portion.
As shown in FIG. 1, a pair of the vertically positioned head bolt 8 and bearing bolt 12 are arranged on the same axis 29. This arrangement enables a pulling force the lower side portion of the inter-cylinder wall 2 receives to act on the same axis 29, which results in the possibility of inhibiting a shear strain of the lower side portion 2b of the inter-cylinder wall 2. This can prevent the seizure of the piston and the production of the slap sound or the like attributable to the shear strain of this portion.
As shown in FIG. 1, the head bolt 8 is made common with the bearing bolt 12. This facilitates the control of bolts and reducing the cost for purchasing the bolts.
As shown in FIG. 1, an oil supply passage 21 is made to pass a space defined between the upper female screw 9 and the lower female screw 13. Owing to this arrangement, the lower side portion 2b of the inter-cylinder wall 2 can be effectively utilized as a wall for forming the oil supply passage 21.
As shown in FIG. 1, the oil supply passage 21 does not communicate with either of the upper female screw 9 and the lower female screw 13. This arrangement results in being able to inhibit the chips produced when working screws, from entering the oil supply passage 21.
As shown in FIG. 1, a hole 23 of an interlocking shaft 22 invades the lower side portion 2b of the inter-cylinder wall 2 between the upper female screw 9 and the lower female screw 13. Owing to this arrangement, the lower side portion 2b of the inter-cylinder wall 2 can be effectively utilized for forming the hole 23.
As shown in FIG. 1, the cylinder block 6 can be divided into an upper block portion 6a and a lower block portion 6b. Owing to this arrangement, it is possible to produce different types of engines separately with ease by preparing a plurality of lower block portions 6b and assembling these lower block portions 6b selectively to the upper block portion 6a. For example, a lower block portion 6b large in width for standard use and another lower block portion 6b small in width for tractor use are prepared. If these lower block portions 6b are selectively assembled to the upper block portion 6a, it is possible to produce an engine for standard use and another engine for tractor use separately with ease.
As shown in FIG. 6, the bearing wall 10 has the lower wall portion 10b connected to the lower block portion 6b. In this arrangement, the gas pressure produced in the combustion chamber is burdened not only by the left and right both sides of the lower side portion 2b of the inter-cylinder wall 2 but also by the upper block portion 6a through the lower block portion 6b. This can reduce the burden applied on the left and right both sides of the lower side portion 2b of the inter-cylinder wall 2.
As shown in FIG. 6, the bearing wall 10 has its lower wall portion 10b connected to the lower block portion 6b. In this arrangement, the butting surfaces of the upper and lower block portions 6a and 6b are sealed through both of block assembling bolts 24 and the bearing bolts 12 to result in exerting a high sealing force.
As shown in FIGS. 4 and 5, the cylinder block 6 has its left and right outer walls 14 curved along external outlines of a connecting rod 25 and a crank arm 26 which pass the vicinity of the left and right outer walls 14. This arrangement affords a high rigidity of the cylinder block 6.
As shown in FIGS. 4 and 5, attaching bosses 28a and 28b of the block assembling bolts 24, 24 are formed in an inner side wall portion 27 which is retreated inwards. The left and right attaching bosses 28a and 28b mutually approach to strengthen the sealing force exerted by the butting surfaces of the upper and lower block portions 6a and 6b. 
As shown in FIG. 4, the lower left and right peripheral wall portions 15, 15 of the cylinder wall 1 are arranged so that they start to increase their thicknesses from their mid portions 15a, 15a in the front and rear direction. This arrangement makes it possible to take a sufficient thickness of each of the left and right peripheral wall portions 15, 15 of the cylinder wall 1 near the inter-cylinder wall 2.
As shown in FIG. 4, both of outwardly facing surfaces 15b, 15b of the left and right peripheral wall portions 15, 15 are arranged to externally flare toward the left and right both sides 2c, 2c from their mid portions 15a, 15a in the front and rear direction. This arrangement makes it possible to take a sufficient thickness of each of the left and right peripheral wall portions 15, 15 of the cylinder wall 1 near the inter-cylinder wall 2.
In the case where both of the outwardly facing surfaces 15b, 15b of the lower left and right peripheral wall portions 15, 15 of the cylinder wall 1 are formed substantially straight as a whole along the front and rear direction, it is possible to take a sufficient thickness of each of the left and right peripheral wall portions 15, 15 of the cylinder wall 1 near the inter-cylinder wall 2 and besides facilitate the molding of the cylinder wall 1.